1. Field of the Invention
The present invention is directed to anaerobic adhesive compositions which include an acrylate component; a coreactant; and an anaerobic cure-inducing composition. The compositions may also include a maleimide component. Reaction products of the compositions of this invention exhibit superior resistance to thermal degradation, particularly under elevated temperature conditions.
2. Brief Description of the Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, "Anaerobic Adhesives" in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker. Inc., New York (1994) and references cited therein. Their uses are legion and new applications continue to be developed.
The patent literature points out examples of related anaerobic adhesives, several of which are discussed here.
For instance, U.S. Pat. No. 4,524,176 (Pike) refers to an anaerobic adhesive which includes the reaction product of an hydroxyl-containing polyester and a glycidyl acrylate. The polyesters which are said to be useful in that composition are reported as having a viscosity at room temperature of between 5,000 to 50,000 cps (col. 2, lines 52-55). The '176 patent also refers to the addition of a modifier--i.e., triallyl cyanurate--to alter flexibility and bond strength of the cured adhesive. Four compositions are recorded which include 10 weight percent triallyl cyanurate (nos. 3-6 in Table III of the '176 patent), each of which are stated as curing at a temperature of 170.degree. C. for a period of time of 30 minutes. The only compositions recorded in Table III which cured at room temperature (requiring 16 hours) (nos. 9-11) do not contain triallyl cyanurate.
U.S. Pat. No. 4,600,738 (Lamm) and U.S. Pat. No. 4,624,725 (Lamm) each refer to a two-component acrylic modified polyester adhesive. The required components are (a) the acrylic modified polyester reaction product of a glycidyl acrylate and a hydroxyl containing polyester and (b) an organometallic acid salt containing a polymerizable monomer, which acts as a primer to enhance the degree to which the acrylic modified polyester adheres to a surface.
U.S. Pat. No. 4,216,134 (Brenner) speaks to one-component anaerobic adhesive compositions which include ethylenically unsaturated diluent monomers (such as styrene, divinylbenzene, diallyl carbonates, diallyl maleate, diallyl phthalate, diallyl isophthalate and the like), prepolymers (such as 1,2-polybutadienes and copolymers thereof, isophthalic polymers, bisphenol A fumates, epoxy resins, polyallylvinyl ethers and the like) and triallyl cyanurate or triallyl isocyanurate as reaction components. Included among the diluent monomers of the '134 patent are polyfunctional acrylates and (meth)acrylates. The '134 patent is at least a three component composition (in addition to its cure components) and requires a prepolymer which may be included in addition to or as a replacement for the ethylenically unsaturated diluent monomer. Examples of the prepolymer are given as "high vinyl 1,2-polybutadienes and copolymers thereof especially styrene; isophthalic polymers; bisphenol A fumates and other alkyls; epoxy resins; polyalkyl vinylethers and related polymers; alkylic resins based on polyfunctional ethers and esters and mixtures of two or more of these prepolymers." (Col. 5, lines 32-39.)
U.S. Pat. No. 4,107,109 (Kassal) refers to a composition for making graft copolymers under anaerobic conditions at elevated temperatures, such as 120.degree. C. to 180.degree. C. The composition includes a solution of certain uncured elastomers in a polymerizable vinyl monomer and a thermally activatable modified peroxide initiator. When polymerized, the elastomer is said to form a continuous phase with the resulting vinyl polymer forming a separate and discrete phase. Bismaleimide, triallyl cyanurate and isocyanurate are noted as optional components which may be employed in the polymerization reaction.
U.S. Pat. No. 5,023,107 (Roberts) refers to a hard tissue surface treatment using a bisbiguanide primer prior to application of an adhesive, which itself may include polymerizable monomers such as glycol dimethacrylate, diallyl phthalate and triallyl cyanurate.
U.S. Pat. No. 3,988,299 (Malofsky) refers to a heat curable composition having improved thermal properties, which includes certain acrylate monomers and maleimide compounds.
And L. J. Baccei and B. M. Malofsky, "Anaerobic Adhesives Containing Maleimides Having Improved Thermal Resistance" in Adhesive Chemicals, 589-601, L- H Lee, ed., Plenum Publishing Corp. (1984) report the use of maleimides--specifically, N-phenyl maleimide, m-phenylene dimaleimide and a reaction product of methylene dianiline and methylene dianiline bismaleimide--to increase the thermal resistance of anaerobic adhesives which are fully cured at temperatures of at least 150.degree. C.
F. J. Campbell et al., "Electron Beam Curing Improves High Temperature Strength of Vinyl Ester Adhesives", Natl. SAMPE Symp. Exh., 59-63 (1977) speaks to radiation curing of acrylic-modified epoxies together in formulations with vinyl functional monomers (i.e., divinyl benzene, triallyl cyanurate and styrene) to form cured resins of higher level cross-linking and superior ambient and elevated temperature performance.
U.S. Pat. No. 4,384,101 (Kovacs) relates to thermosetting resin mixtures which contain epoxide components, isocyanate components, latent-hardening components and triallyl cyanurate as a cross-linking compound.
Notwithstanding the state-of-the-technology, a one-part, anaerobic adhesive composition would be desirable which is capable of curing under ambient environmental conditions, and which, when cured into a reaction product, demonstrates superior properties, such as superior resistance to thermal degradation at elevated temperatures.